Conventionally, composite sheets including an elastic sheet and an inelastic sheet are known. For example, Patent Literature 1 discloses a disposable diaper using, as an important constituent, the composite sheet formed from the elastic sheet and the inelastic sheet. The disposable diaper disclosed therein has the elastic sheet on a skin-contact surface and the inelastic sheet on a non-skin-contact surface. The inelastic sheet is bonded to the elastic sheet being under tension so that the inelastic sheet may get many wrinkles. The wrinkles formed in this manner define clearance gaps between the diaper and clothes, ensuring desired breathability.
Conventionally, methods for manufacturing the composite sheet including the elastic sheet and the inelastic sheet are known. For example, Patent Literature 2 discloses a method for manufacturing the composite sheet including a step of joining a nonwoven fabric layer as the inelastic sheet to an elastic base layer as the elastic sheet with use of an ultrasonic system including an anvil and a horn.